Study On Spatiotemporal Variations And Influencing Factors Of Fractional Vegetation Coverage In Central Yunnan Urban Agglomeration

As the main body of the land ecosystem,vegetation is very sensitive to climate change.And in recent years,the climate of the southwestern region of China has changed significantly.As an important economic center in the Southwest region,the time and space changes in fraction vegetation coverage of central Yunnan urban agglomeration and factors that need to be studied urgently.This paper uses MODIS NDVI data,meteorological data,elevation data,etc.to analyze the temporal and spatial changes and influencing factors of vegetation coverage in the central Yunnan urban agglomeration in the past two decades through trend analysis,spatial analysis,correlation analysis and other methods.The main conclusions are as follows:(1)The average fraction vegetation coverage of urban agglomeration in central Yunnan was 0.569,and the overall trend was increasing trend(0.0028/a).From the perspective of different seasons,the fraction vegetation coverage in autumn was the highest(0.634),spring was the lowest(0.506)but the increase trend was the fastest(0.0052/a).However,the fraction vegetation coverage in summer showed a downward trend(-0.0012/a).From the perspective of different land cover types,the fraction vegetation coverage of grassland(0.0030/a)and forest(0.0028/a)increased the fastest,and the vegetation coverage in urban areas showed a weak downward trend(-0.0013/a).According to the mutation analysis,the vegetation coverage in the study area changed abruptly.(2)The annual average and seasonal changes of fraction vegetation coverage with altitude could be mainly divided into three categories.From the perspective of different slopes,the fraction vegetation coverage in spring,autumn and winter showed an increasing trend with slope.In summer,the fraction vegetation coverage decreased with slope.(3)The mean yearly temperature in the central Yunnan urban agglomeration in the past 20 years showed a decreasing trend(-0.01?/a),while the precipitation showed a decreasing trend(-1.97 mm/a).The average annual vegetation coverage was positively correlated with both temperature and precipitation.(4)The accelerated process of urbanization(190.5 km~2)has increased the urban area and reduced the fraction vegetation coverage(-0.0059/a),the fraction vegetation coverage in rural areas has increased but the area decreased significantly(3969.25 km~2),and human activities such as returning farmland to forests and grasslands have played a role.Under the circumstance of environmental policy protection in Kunming Xishan Forest Park,the overall upward trend of vegetation coverage was 0.006-0.008/10a.(5)The main factor affecting the spatial differentiation of fraction vegetation coverage in the central Yunnan urban agglomeration is vegetation type,but the long-term changes of other factors(such as temperature,precipitation,human activities,etc.)cannot be ignored.In summary,the fraction vegetation coverage of the central Yunnan urban agglomeration generally showed an upward trend,but in the city and its surrounding areas,with the expansion of the city,the vegetation coverage decreased significantly.Except for summer,other seasons showed an upward trend.With the increase of altitude,the fraction vegetation coverage generally decreased.Fraction vegetation coverage was generally positively correlated with both temperature and precipitation.The main factor affecting the spatial differentiation of vegetation coverage in the central Yunnan urban agglomeration is the vegetation type.